Britain's medical regulator finds that Dr. Andrew Wakefield, who now practices in Texas, conducted his now-discredited research on the MMR shot in an unethical and irresponsible manner.

Reporting from London — The British doctor whose suggestion of a link between the MMR shot and autism helped cause vaccination rates to plunge conducted his now-discredited research in a dishonest and irresponsible manner, medical authorities here concluded Thursday.

It was the latest development in a long-running health controversy that has seen measles make a comeback among British children after being all but wiped out.

The General Medical Council, Britain's medical regulator, found that Andrew Wakefield acted unethically in the way he collected blood samples from children and in his failure to disclose payments from lawyers representing parents who believed the vaccinations for measles, mumps and rubella -- given as a single shot, referred to as the MMR vaccine -- had hurt their kids.

The regulator also concluded that Wakefield acted with "callous disregard" by conducting invasive tests on children that were not in their best medical interests.

Wakefield, who now lives and works in the United States, called the allegations "unfounded and unjust" and expressed deep disappointment with the council's finding. He told reporters he had "no regrets" over his work.

In 1998, Wakefield caused a national -- and, later, international -- stir with a study published in the prestigious British medical journal Lancet that suggested a possible link between the MMR vaccine and child autism.

His subsequent, widely publicized comments that he could no longer in good conscience recommend the vaccine to parents caused a dramatic drop in vaccination rates across Britain. A Wakefield appearance on "60 Minutes" helped fuel a vocal anti-vaccination movement in the United States.

His study, however, was based on just 12 children. Lancet later declared that it should not have published the report, and further studies have not been able to replicate Wakefield's results.

Although MMR vaccination rates have begun to recover, Britain has seen a surge in measles among children: more than 1,000 cases in 2008, an increase from several dozen annually a decade earlier.

In its findings, presented Thursday after an investigation that took more than two years, the regulator did not rule on Wakefield's conclusions from his research. But it said his research practices had been unacceptable.

Those included taking blood samples from children at his son's birthday party and paying them each about $8, the regulator found. He also performed spinal taps on children at a hospital without due regard for how they might be affected, it said.

It has not yet been decided whether any disciplinary action will be taken against Wakefield, including revocation of his right to practice medicine in Britain.

Wakefield, who now practices in Austin, Texas, came to London for the council's decision Thursday.

"The allegations against me . . . are both unfounded and unjust," he said, standing amid a small knot of supporters. "It remains finally for me to thank parents whose commitment, whose loyalty has been extraordinary, and I want to reassure them that the science will continue in earnest."